An underground bed or layer of permeable rock, sediment or soil that yields water

Air pollution

Toxic or radioactive gases or particulate matter introduced into the atmosphere, usually as a result of human activity

Acid rain

The precipitation of dilute solutions of strong mineral acids, formed by the mixing in the atmosphere of various industrial pollutants -- primarily sulfur dioxide and nitrogen oxides -- with naturally occurring oxygen and water vapor.

Asbestos

A general name given a family of naturally occurring fibrous silicate minerals. Asbestos fibers were used

mainly for insulation and as a fire retardant material in ship and building construction and other industries,

and in brake shoes and pads for automobiles. Inhaling asbestos fibers has been shown to result in lung

disease (asbestosis) and in lung cancer (mesothelioma). The risk of developing mesothelioma is significantly

enhanced in smokers.

Arsenic

A gray, brittle and highly poisonous metal. It is used as an alloy for metals, especially lead and copper, and is

used in insecticides and weed killers. In its inorganic form, it is listed as a cancer causing chemical under

Proposition 65.

Ambient air

Generally, ambient air refers to air outside and surrounding an air pollution source location. Often used interchangeably with "outdoor air."

Alpha particle

A positivelycharged particle emitted by radioactive atoms. Alpha particles travel less than one inch in the

air and a thin sheet of paper will stop them. The main danger from alpha particles lies in ingesting the

atoms which emit them. Body cells next to the atom can then be irradiated over an extended period of

time, which may be prolonged if the atoms are taken up in bone, for instance - Beta particle, Gamma

radiation

Alluvial deposit

An area of sand, clay or other similar material that has been gradually deposited by moving water, such as

along a river bed or shore of a lake.

Air stripping tower

Air stripping removes volatile organic chemicals (such as solvents) from contaminated water by causing

them to evaporate. Polluted water is sprayed downward through a tower filled with packing materials while

air is blown upwards through the tower. The contaminants evaporate into the air, leaving significantlyreduced

pollutant levels in the water. The air is treated before it is released into the atmosphere.

Aeration

Passing air through a solid or liquid, especially a process that promotes breakdown or movement of

contaminants in soil or water by exposing them to air.

Adverse health effects

Effects of chemicals or other materials that impair one's health. They can range from relatively mild

temporary conditions such as minor eye or throat irritation, shortness of breath or headaches to permanent and serious conditions such as cancer, birth defects or damage to organs.

Acute hazards

Hazards associated with shortterm exposure to relatively large amounts of toxic substances.

Activity of a radioactive isotope

The number of particles or photons ejected from a radioactive substance per unit time.

Activated sludge

A term used to describe sludge that contains microorganisms that break down organic contaminants (e.g.,

benzene) in liquid waste streams to simpler substances such as water and carbon dioxide. It is also the

product formed when raw sewage is mixed with bacterialaden sludge, then stirred and aerated to destroy

organic matter.

Acids

A class of compounds that can be corrosive when concentrated. Weak acids, such as vinegar and citric acid,

are common in foods. Strong acids, such as muriatic (or hydrochloric), sulfuric and nitric acid have many

industrial uses, and can be dangerous to those not familiar to handling them. Acids are chemical

"opposites" to bases, in that they can neutralize each other.

Acetone

A widely used, highly voatile solvent. It is readily absorbed by breathing, ingestion or contact with the skin.

Workers who have inhaled acetone have reported respiratory problems.

Acid deposition

A complex chemical and atmospheric phenomenon that occurs when emissions of sulfur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then deposited on earth in either a wet or a dry form. The wet forms, popularly called “acid rain,” can fall as rain, snow, or fog. The dry forms are acidic gases or particulates.

Accident site

The location of an unexpected occurrence, failure, or loss, either at a plant or along a transportation route, resulting in a release of hazardous materials.

Absorption

The passage of one substance into or through another; e.g., an operation in which one or more soluble components of a gas mixture are dissolved in a liquid.

Abatement

Reducing the degree or intensity of, or eliminating, pollution.

Add-on control device

An air pollution control device such as a carbon adsorber or incinerator that reduces the pollution in an exhaust

gas. The control device usually does not affect the process being controlled and thus is “addon” technology as opposed to a scheme to control pollution by making some alteration to the basic process.

Adaptation

Changes in an organism’s structure or habit that help it adjust to its surroundings.

Acute toxicity

The ability of a substance to cause poisonous effects resulting in severe biological harm or death soon after a single exposure or dose; also, any severe poisonous effect resulting from a single short-term exposure to a toxic substance.

Acute exposure

A single exposure to a toxic substance that results in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day.

Active ingredient

In any pesticide product, the component that kills, or otherwise controls, target pests. Pesticides are regulated primarily on the basis of active ingredients.

Aerobic treatment

Process by which microbes decompose complex organic compounds in the presence of oxygen and use the liberated energy for reproduction and growth. Types of aerobic processes include extended aeration, trickling filtration, and rotating biological contactors.

Adsorption

1. Adhesion of molecules of gas, liquid, or dissolved solids to a surface.

2. An advanced method of treating wastes in which activated carbon removes organic matter from wastewater.

Attenuation

The process by which a compound is reduced in concentration over time, through adsorption, degradation, dilution, or transformation.

Anaerobic

A life or process that occurs in, or is not destroyed by, the absence of oxygen.

Air mass

A widespread body of air that gains certain meteorological or polluted characteristics- for example, a heat inversion or smokiness—while standing in one location. The characteristics can change as the air mass moves away. See

also Inversion

Algal blooms

Sudden spurts of algal growth that can affect water quality adversely and that indicate potentially hazardous changes in local water chemistry.

Algae

Simple rootless plants that grow in sunlit waters in relative proportion to the amounts of nutrients available. They can affect water quality adversely by lowering the dissolved oxygen in the water. Algaeare food for fish and small aquatic animals.

Air pollution episode

A period of abnormally high concentration of air pollutants, often due to low winds and temperature inversion, that can

cause illness and death.

Airborne particulates

Total suspended particulate matter found in the atmosphere as solid particles or liquid droplets. The chemical composition of particulates varies widely, depending on location and time of year. Airborne particulates include windblown dust, emissions from industrial processes, smoke from the burning of wood and coal, and the exhaust of motor vehicles.

Aerosol

A suspension of liquid or solid particles in a gas.

Assimilation

The ability of a body of water to purify itself of pollutants.

Amine

A functional group consisting of "-NH2"

Alkalinity

The capacity of a water to neutralize acids.

Aerobic process

A process which requires molecular oxygen.

Aerobes

Organisms which require molecular oxygen as an electron acceptor for energy production.

Anthropogenic

Anthropogenic Of, made, or caused by human activity or actions.

Anoxic process

A process which occurs only at very low levels of molecular oxygen or in the absence of molecular oxygen.

Anaerobic process

A process which only occurs in the absence of molecular oxygen.

Anaerobes

A group of organisms that do not require molecular oxygen. These organisms, as well as all known life forms, require oxygen. These organisms obtain their oxygen from inorganic ions such as nitrate or sulfate or from protein.

Anabolism

Biosynthesis, the production of new cellular materials from other organic or

inorganic chemicals.

Autotrophs

A group of organisms capable of obtaining carbon for synthesis from inorganic carbon sources such as carbon dioxide and its dissolved species (the carbonates). This group includes plants and algae.

Autotrophic

Organisms which utilize inorganic carbon for synthesis of protoplasm. Ecologists narrow the definition further by requiring that autotrophs obtain their energy from the sun. In microbiologist parlance, this would be a photoautotroph.

Attached growth reactor

A reactor in which the microorganisms are attached to engineered surfaces within the reactor.

Examples of attached growth reactors are the trickling filter and the rotating biological contactor.

Aromatic

A form of bonding in which ring compounds share electrons over more than two atoms. The electrons are delocalized. This leads to unusual ring stability.

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